Device for transmitting signals between moving parts

ABSTRACT

Devices consisting of a signal source and a signal sink connected by a transmission channel for transmitting high-frequency signals, as well as digital signals between moving parts. By eliminating wave reflections, the signals are transmitted such that reliable wide-band transmissions are ensured.

DESCRIPTION

[0001] 1. Field of the Invention

[0002] The invention relates to devices for transmitting high-frequency as well as digital signals between moved parts, consisting of a signal source and a signal sink connected by a transmission channel.

[0003] 2. Prior art

[0004] High-frequency and also digital signals must frequently be transmitted between parts mobile relative to each other. A typical application of such transmission paths is radar technology where signals are transmitted from the transmitter/receiver unit to the antenna. The subject matter of the invention here is the transmission of high-frequency signals such as intermediate-frequency signals or even digital data, rather than the high-performance transmission in the microwave range. Such signals are normally made available as non-symmetrical signals. Various devices are known for transmitting such non-symmetrical signals

[0005] For instance, the transmission may be realised in a capacitive manner by means of a package of plates resembling a variable capacitor. The main problem of this arrangement is the current path between the mutually mobile parts, which is not precisely defined. As a matter of fact, the current flows initially through the plate package. The return path is normally the frame or chassis, mostly implemented as screen or housing. When the parts are rotating relative to each other, however, it is particularly difficult to achieve a sound low-inductance frame or ground connection. This is the reason why the known transmission systems involve inherent problems. It is very difficult here to achieve constant transmission characteristics and a constant cross-talk.

[0006] Even though transmission paths implemented with the aid of variable capacitors are characterised by a comparatively large bandwidth, in distinction from other transmission techniques, they present the disadvantage of a high engineering expenditure in terms of the plate packages and an upper limit frequency which is by far below a wavelength corresponding to the dimensions of the plate package. Another disadvantage of this arrangement is their high sensibility to mechanical loads as well as shocks and vibration.

[0007] Transmission paths based on coupled resonance circuits present good transmission characteristics but naturally they have only a very narrow band. They are also characterised by a high expenditure in terms of manufacturing technology, and possibly require trimming. For different applications each of these elements must be dimensioned differently so that it is hardly possible to realise a wide range of products with such transmission paths in a standard design.

[0008] In order to avoid the disadvantages of these arrangements it has been tried, in several approaches, to improve the high-frequency transmission characteristics of conventional collector rings. Such a method is the simultaneously input of the signals at several locations so that resonance occurs at elevated frequencies only in some operating conditions.

[0009] In another approach an attempt has been made to configure a slip ring with a defined wave resistance and to terminate it with the wave resistor at a suitable location.

[0010] Both approaches are entirely unsuitable for broad-band high-frequency transmission because they start out from a closed annular contact path. This path will always be a capacitive load. Even when a resistor is mounted which corresponds to the wave resistor a closed ring can never be designed to be free of reflection. The reasons why this is not possible will now be explained with reference to FIG. 4 and FIG. 5.

[0011]FIG. 4 shows a closed ring which is designed with a wave resistor of Z₀=50 Ω. A real resistor 2 with R=50 Ω is mounted on this wave resistor. FIG. 5 now shows a small segment of the ring including the real resistor. On the assumption that the ring is actually terminated and free of reflection a wave propagating along the direction 3 would meet an impedance ahead of the resistor 2, which is the result of the parallel mounting of the real resistor with R=50 Ω and the line with Z₀=50 Ω for continuing conduction behind the resistor. The value of the parallel circuit were hence 25 Ω. As a result, the line cannot be free of reflection for the wave ahead of the resistor. Even with all other combinations of wave resistors and terminating resistors a line free of reflection cannot be realised here.

[0012] The aforedescribed non-contact transmission methods excel themselves over the contacting methods by a negligible mechanical friction and hence the lack of abrasion or contact wear. The service life of such non-contact transmission systems is essentially longer than that of the contacting methods, particularly in the case of high speeds in the relative motion of the moving parts. All these transmission methods involve, however, the inherent disadvantage that they have a lower limit frequency. As a function of the engineering design this limit may vary. What is characteristic, however, is the fact that a common-mode component with frequency 0 cannot be directly transmitted.

[0013] The digital signals occurring in practical industrial application, e.g. the signals used in advanced bus systems, vary between almost static signals with extremely low frequencies and signals with a maximum clock rate predetermined by the bus system. The lowest frequencies occurring are mostly below the lower limit frequency of the aforedescribed non-contact transmission systems.

[0014] Hence a direct transmission of these signals is, as a rule, not possible. The known modulation or coding methods are a remedy in this respect. Both methods require a high engineering expenditure. The coding methods which are well suitable for digital signal transmission, in particular, such as the Manchester coding approach, require a wider bandwidth of the transmission channel merely on account of their coding. As a result the expenditure and costs of the transmission path are increased. Moreover, the timing of the digital signal is required in the majority of coding applications. This timing can frequently not be reconstructed from the signal as such. Only with a suitable data structure timing regeneration is possible by means of PLL elements. Such circuits are mostly suitable for a previously determined data rate. In the event that the non-contact transmission path should be transparent in terms of data and protocol only the expensive modulation methods can frequently be employed only.

DESCRIPTION OF THE INVENTION

[0015] The invention is now based on the problem of improving a device for transmitting signals between mobile elements consisting of a signal source and a signal sink connected by a transmission channel in such a way that a reliable wide-band transmission will be ensured, without a frame or ground connection being required between the moving parts. In particular devices should be defined here which are suitable for transmitting high-frequency signals and/or digital signals. Moreover, a transmission transparent in terms of protocol and data with a data rate lower than the lower limit frequency of the transmission path for the transmission of digital signals should be possible with a low engineering expenditure and without an increased requirement in terms of bandwidth.

[0016] Solutions to the problem underlying the invention are defined in claims 1, 7 and 12. Expedient improvements of the invention are the subject matter of the dependent claims.

[0017] In accordance with the present invention a device according to the introductory clause of claim 1 is so configured that the transmission path has a symmetrical structure and hence a precisely defined current path is available. The current paths for emission and return are realised in approximately identical ways. The signal flow must hence not be returned via another path which is poorly defined. Hence poor frame or ground connections are irrelevant and a frame or ground connection may even be eliminated entirely. As a result, a separation of potentials of the parts movable relative to each other can be achieved at the same time. Due to the symmetrical transmission moreover an excellent in-phase rejection is achieved. This is particularly expedient specifically in those cases which involve a poor ground connection between the moving parts so that substantial differences in voltage may be present between these elements.

[0018] In a particularly expedient configuration optional matching circuits are provided for a conversion of non-symmetrical into symmetrical signals and vice versa. Such matching circuits are necessary when the signal source or even the signal sink operate on non-symmetrical signals.

[0019] Another design consists in the provision that the coupler means consist of two pairs of facing conductive surfaces. The conductor surfaces should be so designed that they are matched with the path of travel and that always the widest overlapping possible of the conductive surfaces will be present on the moving parts. The individual conductor surfaces of each pair should be symmetrical as far as this is possible so as to ensure the symmetry of the arrangement as a whole.

[0020] In a further embodiment the matching circuits are implemented by means of passive components. For instance, several circuits for impedance matching and symmetrization by means of lines and also with transformers are known. Here, too, designs using other passive components are, of course, possible here, too.

[0021] Another embodiment of the arrangement according to claim 1 is characterised by the application of active components in the matching circuits. The functions of these matching circuits invention can be implemented by the use of semiconductors and integrated amplifiers without any problems.

[0022] Moreover, the first matching circuit can be implemented by means of an amplifier having an inverting and a non-inverting output. Two separate amplifiers are, of course, equally suited for application. The second matching circuit can hence be implemented likewise by means of a differential amplifier.

[0023] In a further embodiment of the arrangement according to claim 1 for the transmission of digital information a logic gate with an inverting and a non-inverting output is used in the first matching circuit. Here, too, two separate logic gates may equally be employed. The second matching circuit may be implemented by means of a logic circuit having a differential input.

[0024] In an inventive further arrangement according to the introductory clause of claim 1 and the characterising clause of claim 7, the broad-band signal transmission characteristics of a line terminated to be free of reflection are utilised. Such a line may be structured, in correspondence with prior art, as coaxial line, strip line or as symmetrical two-wire circuit. As a matter of fact, other types of lines are suitable as well for guiding electromagnetic waves, which have a constant defined wave resistance over the entire length and which are terminated on at least one end with a resistor corresponding to the wave resistance so as to be free of reflection. The essential aspect, however, is the transmission of TEM waves on electrical lines.

[0025] As a rule, such lines are terminated on both ends with the wave resistor. However, a signal source with a non-matched internal resistance may equally be connected to a line which, on its part, is terminated with a resistor corresponding to the wave resistance so as to be free of reflection. Reflection cannot occur on the termination free of reflection. With a circular arrangement of such a line in correspondence with the path of the rotating movement the information may be tapped along the line.

[0026] In the illustration of the inventive arrangement according to claim 7 reference is made to the term of line. As a matter of fact, it relates to all lines, of course, also in the case of several lines. The term of rotating movement refers to a rotating motion over any angular range whatsoever and hence even applies to limited angular ranges up to continuous rotating movements.

[0027] In a particularly expedient embodiment the signals are coupled out of this line via a high-impedance output circuit which does hence not give rise to reflections at the out-coupling site. Such an output circuit may utilise a transformer or even an amplifier with a high-impedance input or an impedance transformer,

[0028] In a further expedient configuration the signal is coupled out by means of a field probe. This probe may be both an E-field probe or an H-field probe or even a combination of both types and equally a second coupled line. What is essential in the design of the field probe is the aspect that it will not take an influence on the field of the line in a way which will create reflections on the line. An attenuation of the signal on the line by the probe is permissible since here any further reflections do not occur.

[0029] In another embodiment of this inventive arrangement according to claim 7 signals may be coupled into the line even with contact. To this end it is necessary, however, to terminate the line on both ends in a form free of reflection as waves propagate from the rotatable input site along both directions of the line.

[0030] In a further design signals are coupled into the line via a coupler element which achieves the coupling of the E-fields and/or the H-fields. In the simplest form this coupling element may be another line arranged in parallel with the first line.

[0031] In accordance with claim 12, an inventive device is configured, specifically for the transmission of digital signals, in a way that the transmitter is provided with a signal processing circuit which increases the slope of the signal flanks of the digital signal supplied by the data source in such a way that the reciprocal values of the rise time and the drop time are each higher than the lower limit frequency of the transmission path, whilst furthermore a logic evaluation circuit is provided in the receiver which reconstructs the original signals from the pulses supplied by the transmission path by differentiation of the signals emitted by the transmitter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The invention will be described in the following by exemplary embodiments with reference to the drawings wherein:

[0033]FIG. 1 illustrates an inventive arrangement according to claim 1,

[0034]FIG. 2 shows a practical implementation of the coupler means according to claim 1,

[0035]FIG. 3 is a schematic view of an inventive arrangement according to claim 7,

[0036]FIG. 4 shows a transmission system according to prior art,

[0037]FIG. 5 is a detail of the illustration in FIG. 4,

[0038]FIG. 6 represents a schematic arrangement of an inventive transmission path according to claim 12,

[0039]FIG. 7 is a schematic view of a transmission path according to prior art,

[0040]FIG. 8 shows a schematic view of the receiver unit, and

[0041]FIG. 9 is a graph representing the signals in a time/amplitude diagram.

[0042]FIG. 1 shows an inventive arrangement according to claim 1, which consists of a signal source and a signal sink 5 connected by the first matching circuit 2, the coupler means 3 and the second matching circuit 4.

[0043]FIG. 2 illustrates a practical implementation of the inventive coupler means, Two conductor surfaces 8 and 9 or 10 and 11, respectively, of approximately the same size are arranged by means of holding elements 6 and 7 on the two parts which may be moved relative to each other. The arrow indicates the principal direction of movement. With movements along this direction the quality in transmission remains constant. With movements in all other directions the quality in transmission is subject to very strong variations.

[0044]FIG. 3 illustrates an inventive arrangement according to claim 7. A transmission path for signal transmission, consisting of a transmitter and/or receiver 12 as well as of a receiver and/or transmitter 13 for relative rotation, is provided here, which exchange signals by means of a line 14 which is terminated by an impedance 15 in correspondence with its wave resistance.

[0045]FIG. 4 shows an arrangement corresponding to prior art. It is composed of a transmitter and/or receiver 12 with a line 14 closed to form a ring, which is connected to a terminating resistor 15. The signals are transmitted to the receiver and/or transmitter 13 in relative rotation mostly by a galvanic contact with the line 14.

[0046]FIG. 5 serves to explain the impedance situation in an arrangement according to FIG. 4 in correspondence with prior art. On the assumption that the line ring is terminated in correspondence with its wave resistance, an electromagnetic wave which propagates along the direction 16 meets a parallel circuit including the impedances of the line ring 14 and the terminating resistor 15. The total impedance value is, in any case, smaller than the impedance of the line ring and hence provides for mismatching.

[0047]FIG. 6 is a view of an inventive arrangement according to claim 12, which consists of a data source 1 and a data sink 5, which are both interconnected via the transmitter 2, the transmission path 3 and the receiver 4. The transmitter includes a signal processing circuit 21 so as to ensure a minimum slope of the signal flanks. An evaluation circuit 41 is provided in the receiver, which reconstructs the original signal from the signal which has been distorted by the transmission path.

[0048] The transmitter 2 is provided with a signal processing circuit 21. This circuit increases the flank slope of the digital signals furnished by the data source in such a way that the reciprocal values of the rise and drop times are each greater than the lower limit frequency of the transmission path. The signals so processed are then emitted by the transmitter to the transmission path 3. On account of the band-pass characteristic of the transmission path only isolated pulses arrive still at the receiver 4, which assume positive or negative values, depending on the flank emitted by the transmitter. An evaluation circuit 41 is provided in the receiver, which now reconstructs the original signal from these pulses again. The signal so reconstructed is then transmitted by the receiver to the data sink. In an expedient embodiment of the invention the evaluation circuit includes a first comparator for detecting negative pulses. A digital memory is set by the first comparator and reset by the second comparator. As a result, the polarity of the pulse occurred last is stored. With the pulses occurring only at signal flanks they are indicative of variations in the signal level. As these variations are stored the output of this memory reflects the last signal level.

[0049]FIG. 7 shows an arrangement in correspondence with prior art. It consists of a data source 1, a transmitter 2, a transmission path 3, a receiver 4 as well as of a data sink 6.

[0050]FIG. 8 illustrates a typical structure of the signal processing circuit in the receiver. This circuit includes a first comparator 42 for detecting positive pulses as well as a second comparator 43 for detecting negative pulses. The output signals of the two comparators are combined with each other by means of a storage element 44.

[0051]FIG. 9 is explanatory of the mode of operation of the inventive arrangement according to claim 12. The graph (a) is representative of a typical signal as supplied by the data source. This signal is not processed by the signal processing circuit in the transmitter in a way that the minimum slope of the signal flanks will be ensured. This signal is represented by graph (b). Downstream of the transmission path with band-pass characteristic the signal presents the shape (c). Now the receiver must reconstruct the original signal by means of an evaluation circuit. When the signal is now integrated by means of an integrator, in correspondence with one embodiment of the invention, the signal shape according to graph (d) is obtained. With another embodiment of the invention the evaluation is performed by means of two comparators and a memory. The graph (e) represents the output signal of the first comparator for detecting positive pulses whilst graph (a shows the output signal of the second comparator for detecting negative pulses. The output signal of the memory is represented by graph (g). 

1. Arrangement for signal transmission between two parts mobile relative to each other, consisting of a signal source and a signal sink, which are connected by a transmission channel, characterised in that a symmetrical coupler means is provided in the signal path of said transmission channel, which transmits the symmetrical signal from the signal source between said parts mobile relative to each other.
 2. Arrangement according to claim 1, characterised in that in the signal path of said transmission channel optionally a first matching circuit is arranged ahead of said transmission channel, which converts the signal from said signal source into a symmetrical signal, and that furthermore optionally a second matching circuit is arranged downstream of the transmission channel, which re-converts the non-symmetrical signal again into a symmetrical signal.
 3. Arrangement according to claim 1 or 2, characterised in that said symmetrical coupler means consists of two conductive surfaces for signal emission of approximately the same size, and of two conductive surfaces for signal reception of approximately the same size, which are arranged in the immediate vicinity of said first surfaces.
 4. Arrangement according to claim 3, characterised in that said conductive surfaces for signal emission have other dimensions than or the same dimensions as the conductive surfaces for signal reception.
 5. Arrangement according to any of the claims 1 to 4, characterised in that said first matching circuit and/or said second matching circuit is optionally implemented by means of passive components such as transformers and lines or by means of active components such as semiconductors and amplifiers.
 6. Arrangement according to the claims 1 to 5, characterised in that said first matching circuit is optionally implemented by means of an amplifier and/or a logic gate with an inverting and a non-inverting output, and/or the second matching circuit is optionally implemented by means of a differential amplifier or a logic circuit having a differential input.
 7. Arrangement according to the introductory clause of claim 1, characterised in that at least one line is provided in the signal path of said transmission channel, which is terminated, at least on one end, with a resistor corresponding to its wave resistance so as to be free of reflection, and supplies said receiver and/or is optionally supplied by the transmitter.
 8. Arrangement according to claim 7, characterised in that in the signal path of said transmission channel the signals are coupled out of the line via a high-impedance output circuit and/or via a field probe which does not cause any additional reflections on the line.
 9. Arrangement according to claim 8, characterised in that in the signal path of said transmission channel the signals are coupled into the line in a contacting manner, and that at the same time the line is terminated on both ends in correspondence with its wave resistance so as to be free of reflections.
 10. Arrangement according to claim 8, characterised in that in the signal path of said transmission channel the signals are coupled into the line via a coupler element which couples signals into the line via electrical and/or magnetic fields.
 11. Arrangement according to any of the claims 1 to 10, characterised in that the signals to be transmitted are high-frequency signals.
 12. Device for non-contacting transmission of signals between moving parts, consisting of a data source for generating the signals, a transmitter which transmits these signals to the receiver by means of a non-contacting transmission path with band-pass characteristic, and a data sink which receives the data from the receiver, characterised in that said transmitter is provided with a signal processing circuit which increases the slope of the signal flanks of the signal supplied by said data source in such a way that the reciprocal values of the rise and drop times are each higher than the lower limit frequency of the transmission path, and that moreover an evaluation circuit is provided in said receiver which reconstructs the original signals from the pulses supplied from said transmission path, which are generated by a differentiation of the signals emitted by said transmitter.
 13. Device according to claim 12, characterised in that said evaluation circuit comprises an integrator which integrates the pulses arriving from said transmission path and which passes the signal so integrated on to said data sink.
 14. Device according to claim 12 or 13, characterised in that in said evaluation circuit a first comparator is provided for detecting positive pulses and a second comparator is provided for detecting negative pulses, as well as a memory element which is connected to both comparators and stores the polarity of the pulse which occurred last, using the output signals of said comparators, and passes a signal to said data sink in correspondence with the condition as stored.
 15. Device according to claim 12 or 13, characterised in that the signals to be transmitted are digital signals. 